#include <iostream>
using namespace std;
int main()
{
int a1,a2,n,s;
cin>>a1>>a2>>n;
s=a1+(a2-a1)*(n-1);
cout<<s<<endl;
return 0;
}
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#include <iostream>
using namespace std;
int main()
{
int a1,a2,n,s;
cin>>a1>>a2>>n;
s=a1+(a2-a1)*(n-1);
cout<<s;
return 0;
}

include<iostream>
#include<iomanip>
#include<cmath>
#include<bits/stdc++.h>
#include<cstdio>
#include <stdio.h>
int main()
{
int a1,a2,n,d,last; //d为公差，last为末项,n为项数
scanf("%d %d %d",&a1,&a2,&n);
d = a2-a1;
last = a1 + d*(n-1);
printf("%d\n",last);

return 0;
}

#include<iostream>
using namespace std;
int main(){
    long long a1, a2, n;
    cin >> a1 >> a2 >> n;
    cout << a1+(n-1)*(a2-a1);
    return 0;
}

#include<iostream>
using namespace std;
int main()
{
int a1,a2,n,d,last;
cin>>a1>>a2>>n;
d=a2-a1;
last=a1+d*(n-1);
cout<<last;
return 0;
}

#include<iostream>
#include<iomanip>
#include<cmath>
#include<ctime>
using namespace std;
int main()
{
int a2,a1,n,X;
cin>>a1>>a2>>n;
X=a1+(a2-a1)*(n-1);
cout<<X;
return 0;
}

include<iostream>
#include<iomanip>
#include<cmath>
#include<bits/stdc++.h>
#include<cstdio>
#include <stdio.h>
int main()
{
int a1,a2,n,d,last;
scanf("%d %d %d",&a1,&a2,&n);
d = a2-a1;
last = a1 + d*(n-1);
printf("%d\n",last);

return 0;
}